The bucket an s3 repository is configured with will no longer be created automatically.
It must exist before the s3 repository is created.

Support for specifying s3 credentials through environment variables and
system properties has been removed. Use the elasticsearch-keystore tool
to securely store the credentials.

Specifying region has been removed. This includes the settings cloud.aws.region,
cloud.aws.s3.region, repositories.s3.region, and specifying
region inside the repository settings. Instead, specify the full endpoint if a custom
s3 location is needed, or rely on the default behavior which automatically locates
the region of the configured bucket.

Specifying s3 signer type has been removed, including cloud.aws.signer and cloud.aws.s3.signer.

Global repositories settings have been removed. This includes repositories.s3.bucket,
repositories.s3.server_side_encryption, repositories.s3.buffer_size,
repositories.s3.max_retries, repositories.s3.use_throttle_retries,
repositories.s3.chunk_size, repositories.s3.compress, repositories.s3.storage_class,
repositories.s3.canned_acl, repositories.s3.base_path, and
repositories.s3.path_style_access. Instead, these settings should be set directly in the
settings per repository.
See S3 Repository settings.

The container an azure repository is configured with will no longer be created automatically.
It must exist before the azure repository is created.

Global repositories settings you are able to set in elasticsearch config file under repositories.azure
name space have been removed. This includes repositories.azure.account, repositories.azure.container,
repositories.azure.base_path, repositories.azure.location_mode, repositories.azure.chunk_size and
repositories.azure.compress.
You must set those settings per repository instead. Respectively account, container, base_path,
location_mode, chunk_size and compress.
See Azure Repository settings.

The icu4j library has been upgraded to 59.1,
Indices created in the previous major version will need to be reindexed
in order to return correct (and correctly ordered) results,
and to take advantage of new characters.

Previously, plugins could construct an Environment instance from Settings to
discover the path to plugin-specific config files. This will no longer work in
all situations as the Settings object does not carry the necessary information
for the config path to be set correctly. Instead, plugins that need to know the
config path should have a single constructor that accepts a pair of Settings
and Path instances, and construct an Environment using the corresponding
constructor on Environment.